Determination of caprine serum albumin in milk using bromocresol green dye

Abstract

The objective of this study was to develop and validate a colorimetric assay to measure caprine serum albumin (CSA) concentrations in milk. The principle of the say was based on the bind-ing of albumin to bromocresol green (BCG) dye at pH 4.0. The absorption of the dye-albumin complex was determined spectrophotometrical-ly at 640 nm. A linear relationship existed be-tween CSA concentrations (0.01 to 8.0 mg/ml) and absorbance values. Intra-assay and inter-assay coefficients of variation for the proposed assay were 2.6% and 12% respectively. Recov-ery from milk samples spiked with albumins was 89.15% ± 7.6%. The developed assay was vali-dated using 126 milk samples collected from lactating Saanen goats at various stages of lac-tatio. Caprine serum albumin concentrations in milk ranged between 0.31 and 0.52 mg/ml. The concentrations of CSA were significantly higher (p < 0.05) at the beginning of lactation, declined rapidly and remained relatively stable in mature milk. Caprine serum albumin correlated posi-tively (p < 0.05) with milk somatic cell counts, total solids, protein, fat and whey and correlated negatively (p < 0.05) with milk lactose and casein concentrations. It was concluded that the pro-posed BCG dye-binding method is easy to per-form, rapid, sensitive, reliable and can be used to determine CSA concentrations in milk col-lected from goats under different physiological conditions.